1. Field of the Invention
The invention relates to a universal serial bus (USB) device, and more particularly, to a USB device to be initialized with a real descriptor stored in a USB host, and a method for initializing the same.
2. Description of the Related Art
A USB device is an interfacing device for connecting peripheral equipments, such as a keyboard, a monitor, a mouse, a printer, a modem, a digital camera, etc., to a USB host. The USB device is initialized to allow the peripheral equipments to communicate with the USB host. Meanwhile, the USB host stores a real descriptor and a descriptor recognizing program to initialize the USB device.
FIG. 1 is a block diagram of a conventional USB device. In the conventional USB device shown in FIG. 1, a descriptor read/write portion 12 of a USB interface 10 reads a descriptor REDES stored in an additional memory 20 and then, transfers the descriptor REDES to a register 14. The transferred descriptor REDES is stored in the register 14. The descriptor REDES includes the information of a real vendor I.D. and a real product I.D. for a USB host 1.
An initialization signal generator 18 in the USB interface 10 activates an initialization signal XINT, and a voltage regulator 30 pulls up a signal line 40, in response to the initialization signal XINT. That is, a transistor 32 in the voltage regulator 30 is turned on, and then a terminal voltage VDD is transferred to the signal line 40 through a resistor 34.
The descriptor read/write portion 12 reads the descriptor REDES stored in the register 14 at need, and provides the descriptor REDES to the USB host 1 through a USB core 16 and the signal line 40. When a descriptor recognizing program 1a of the USB host 1 recognizes the descriptor REDES provided from the USB interface 10, the initialization of the conventional USB device is completed.
Generally, the additional memory 20 is a ROM (Read Only Memory) positioned at an outside of the USB interface 10, so that the descriptor REDES can be changed depending on the USB host 1.
However, the conventional USB device has disadvantages in points of the chip size and the manufacturing cost due to the additional memory 20 positioned at the outside of the USB interface 10.